Is there any way to darken porcelain Veneers?

Most likely there is residue from the bonding cement. The back of your tooth should feel the same as prior to treatment. There will be a difference, however, in how the smooth porcelain would feel vs natural tooth structure. But, to me this sounds like you should return to the dentist to...

Thanks for the photo, it is helpful. It is possible there is breakdown in the veneer bonding attributing to the color change. Or maybe be time for a new veneer. This is my personal opinion and not a diagnosis.

Zyrconia crowns for a Smile makeover this could be your best desicion,this type of cases you can certainly improve the way you look,changing shape, size and color,also the gum contour can be modify so you will have spectacular results, that smile that you always wanted,yes it can be done with...